The skull of a newly discovered 325-million-year-old shark-like species suggests that early cartilaginous and bony fishes have more to tell us about the early evolution of jawed vertebrates‚Euro"including humans‚Euro"than modern sharks do, as was previously thought.

The new study, led by scientists at the American Museum of Natural History, shows that living sharks are actually quite advanced in evolutionary terms, despite having retained their basic "sharkiness" over millions of years.

"Sharks are traditionally thought to be one of the most primitive surviving jawed vertebrates. And most textbooks in schools today say that the internal jaw structures of modern sharks should look very similar to those in primitive shark-like fishes," Alan Pradel, a postdoctoral researcher at the Museum and the lead author of the study said.

"But we've found that's not the case. The modern shark condition is very specialized, very derived, and not primitive," he said.

The new study is based on an extremely well-preserved shark fossil collected by Ohio University professors Royal Mapes and Gene Mapes in Arkansas, where an ocean basin once was home to a diverse marine ecosystem.

The heads of all fishes‚Euro"sharks included‚Euro"are segmented into the jaws and a series of arches that support the jaw and the gills. These arches are thought to have given rise to jaws early in the tree of life.